Electric relay



June 26, 1934.

ELECTRIC RELAY Filed Jan. 21, 1932 W. D. COCKRELL ET AL Inventors:William D. Cockrell,

Pieter JuchCer;

Their Attorney.

Patented June 26, 1934 ELECTRIC RELAY William D. Cockrell, Schenectady,and Pieter J uohter, ScOtia,

N. Y., assignors to General Electric Company, a corporation of New YorkApplication January 21,

1932, Serial No. 587,944

7 Claims. (01. 250-415) Our invention relates to alternating currentrelay apparatus including a variable rectifying resistance controlelement and an electron discharge amplifier and it is the object of ourinvention to provide an improved form of such apparatus wherein greatersensitivity is obtained. Our invention is particularly applicable tothat form of such apparatus in which the control element isa'photo-electric tube, the apparatus operating in response to variationsof light reaching the tube.

Our invention will be better understood from the following descriptiontaken in connection with the accompanying drawing, and its scope will bepointed out in the appended claims.

Referring to the drawing, Fig. 1 is a circuit diagram illustrating thepreferred form of our invention; and Fig. 2 is a circuit diagram showinga modification.

In the drawing, alternating current for the operation of the apparatusis shown supplied thereto, by way of example, through the transformer 1having a primary winding 2 and a secondary comprising the three windings4, 5, and 6. In the arrangement illustrated, winding 4 supplies thecontrol device '7, winding 5 supplies cathode heating current for theelectron discharge amplifier 8 and winding 6 supplies current to theoutput or load circuit of the amplifier. Control device '7 may be anysuitable variable rectifying resistance device. In the form illustratedthis device is represented as a photo-electric tube which through theleads 9 and 10 is connected with the secondary winding 4 to form aseries circuit including the capacitor 11 whose capacitance may, by wayof example, be of the order of .0002 mi. and resistor 12 whoseresistance may, by way of example, be of the order or" 10 to 20 megohms.The tube '7, it will be noted, is arranged with its cathode connectedwith the resistor 12. The cathode 14 of the amp ifier 8 connects throughthe midpoint of winding 5 with the adjustable arm 15 of potentiometer 16which bridges the winding 4 and is grounded at one end as shown. Theoutput or load circuit of amplifier 8 includes the transformer winding 6and the winding of the relay 20 connected together in the well knownmanner. The control grid 17 of amplifier 8 connects with theabove-mentionedseries circuit at the point 18 which is between theresistor 12 and the control device 7. This grid connection includes theresistor 19 which, by way of example, may have a value of severalmegohms.

With the apparatus arranged as shown and as described above theamplifier 8 having a rectifying characteristic permits current to passvin the load circuit only during that half wave, which for conveniencewill be termed the positive half, which makes the anode positive withrespect to the cathode. The winding 4 is wound in the same manner aswinding 6 so that the polarity of its ends follows the polarity of thecorresponding ends of that winding. It the resistance of the controltube '7 is infinite, that is, if no light is falling upon it, the grid17 receives no positive charge from winding 4 during the positive halfcycle and remains sufliciently negative to render the amplifier 8inoperative to pass the necessary current to cause the operation ofrelay 20. When the resistance of tube 7 is lowered as when light fallsupon it, the grid 17 is rendered less negative or more positive by anamount proportional to the lowered resistance of tube 7. Thus theamplifier 8 passes current in proportion to the decrease in resistanceof 7 or the amount of light falling upon it. During each negative haltcycle when the polarity of winding 4 is reversed, the grid is madepositive by reason of its connection through resistors 19 and. 12 andthe capacitor 11 with the left hand end of winding 4 which at that timeis positive. Since the grid 17 is positive with respect to the cathode14 a grid current flows through resistors 19 and 12 during the negativehalf cycle charging the capacitor 11 until the grid and cathode havesubstantially the same potential. When at the end of this half cycle thecurrent again reverses, the capacitor 11 first discharges throughresistor 12 and tube '7, this being possible since the cathode of thetube connects with the resistor 12. Without the resistor 12 thepotential of the point 18 with respect to the cathode and consequentlythat of grid 1'7 would follow the potential of the adjacent plate of thecapacitor during the interval of discharge with the result that by thetime that the grid potential became sufficiently positive to cause theamplifier to pass current necessary for the operation of relay 20 thecurrent in the alternating current circuit would be well ad vanced inthe positive half cycle. We have found that by providing the resistor 12between capacitor 11 and the point 18 we can cause the amplifier 8 topass the necessary current earlier in each positive half cycle. Thedischarge current from the capacitor 11 produces an IR drop in theresistor 12 and thus renders the point 18 and hence grid 1'7 lessnegative or more positive, however it may be considered, thus causingthe amplifier to begin passing current necessary for the opera,-

tion of the relay earlier in each positive half cycle.

When the leads 9 and 10 to the device 7 are long so that there is arelatively large capacitance between the leads and between the cathodelead 9 and ground which capacitances are represented diagrammatically bythe dotted capacitors 22 and 23 respectively, we have found it to bedesirable to employ the resistor 19 in the grid connection therebylimiting the grid current which charges these leads. When the leads areshort, however, the resistor 19 and the ground connection may beomitted.

In the modification illustrated by Fig. 2 the arrangement of apparatusis similar to that shown in Fig. l the principal difference being thatthe control device 7 is connected between the point 18 and anintermediate point in the secondary winding 6. The apparatus shown inFig. 2 operates in a manner similar to that already described above inconnection with Fig. l and hence a detailed description of this modifiedform is thought to be unnecessary.

We have chosen the particular embodiments described above asillustrative of our invention and it will be apparent that various othermodifications may be made without departing from the spirit and scope ofour invention which modifications we aim to cover by the appendedclaims.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In combination, a source of alternating current, a variablerectifying resistor and a capacitor connected in a ser'es circuit, anelectron discharge amplifier operable from said source and having acontrol grid connected with said series circuit and an impedance in saidgrid connection for limiting the fiow of grid current which charges saidcapacitor and the circuit connections of said resistor.

2. In combination, a source of alternating current, a photo-electrictube having capacitative leads and a capacitor connected in a seriescircuit, an electron discharge amplifier operable from said source andhaving a control grid connected with said series circuit between thecapacitor and the tube and a resistor in said connection for limitingthe grid current supplied to the capacitor and to said leads.

rectifying resistor and a resistor in said grid connection.

4. In combination, a transformer having a plurality of secondarywindings, a capacitor, a resistor and a photoelectric tube connected ina series circuit with one of said windings, an electron discharge devicehaving a cathode operatively connected with an intermediate point ofsaid one winding and a control grid connected with said series circuitbetween the resistor and the tube, a resistor in said grid connectionand a load device connected with another of said secondary windings inthe output circuit of said amplifier.

5. In combination, a source of alternating current, a grid controlledelectron discharge amplifier having an anode-cathode circuit connectedto be supplied from said source and constructed to pass current duringthe positive half cycles only of the source, a variable impedance, meansfor supplying a positive charge to said grid from said source controlledby said impedance during the positive half cycles, means comprising acapacitor for supplying a positive charge to the grid from said sourceduring the negative half cycles and means for producing a voltage dropbetween the capacitor and the grid.

6. In combination, a source of alternating current, a grid controlledelectron discharge amplifier having an anode-cathode circuit connectedto be supplied from said source and constructed to pass current duringthe positive half cycles only of the source, means for supplying apositive charge to said grid from said source during the positive halfcycles, a photo-electric device arranged to control the supply of saidcharge, means including a capacitor for supplying a positive charge tothe grid from said source during the negative half cycles and a resistorarranged to produce a voltage drop between the capacitor and the rid.

7. In combination, a transformer having a plurality of secondarywindings, a grid controlled electron discharge device having ananode-cathode circuit connected with cne of said windings, aphoto-electric tube and a capacitor connected in a series circuit acrossthe other of said windings, a connection between said cathode and anintermediate point of said other winding, a con nection between the gridand said series circuit at a point thereof between the photo-electrictube the capacitor and a resistor in said series circuit between saidpoint and the capacitor.

WILLIAM D. COCKRELL. PIETER JUCHTER.

